1. Field of the Invention
The present invention relates to a spatial transmission optical transceiver (transmitter/receiver) for transmitting/receiving optical signals through space serving as a medium between terminal devices in a network in which a plurality of terminal devices are connected to one another through a serial bus.
Here, the serial bus is used a high-speed serial bus which is standardized in IEEE (The Institute of Electrical and Electronics Engineers) 1394 (xe2x80x9cIEEE Standard for a High Performance Serial Busxe2x80x9d, IEEE Inc., 96.8).
2. Description of the Related Art
A requirement for transmitting a huge mass of data between equipments is now increasingly enhanced in connection with recent enhancement of processing capabilities of computers and increasing requirements for handling a mass of data which are represented by motion pictures. FIG. 10 is a block diagram showing a network using IEEE1394.
In FIG. 10, the respective terminal devices are connected to one another through a feeder-affixed twisted pair line 82 into which a transmission path based on the IEEE1394 standard and a feeder are unified, and each terminal device applies a bias voltage to a twisted pair line. When a feeder-affixed twisted pair line is inserted into or removed from a terminal device, the terminal device concerned detects variation of the bias voltage to detect the insertion/removal of the feeder-affixed twisted pair line and transmits a reset signal to initialize an IEEE1394 network.
FIG. 11 is a block diagram showing the construction of a optical transceiver disclosed in Japanese Laid-open patent Application No. Hei-10-41898 which uses an optical fiber as a part of the transmission path. The optical transceiver is connected to a terminal device through a feeder-affixed twisted pair line based on the IEEE1394 standard, and an optical fiber can be used for a part of the transmission path of the IEEE1394 network.
The operation of the optical transceiver will be described hereunder.
In FIG. 11, the optical transceiver used through the optical fiber comprises a bias circuit 91, a code conversion circuit 92, a peak hold circuit 93, a optical transmitter 94, a optical receiver 95, a power circuit 96, an electrical connector 98 to which a feeder-affixed twisted pair line 97 based on the IEEE1394 standard is connected, and an optical connector 910 to which an optical fiber 99 is connected.
The optical transmitter 94 converts an electrical signal from the code conversion circuit 92 to an optical signal, and transmits the optical signal thus converted through the optical connector 910 onto an optical fiber 99b. The optical transmitter 94 has a function of converting the optical signal received by the optical connector 910 to an electrical signal, performing waveform shaping and then outputting it to the code conversion circuit 92 and the peak hold circuit 93.
The feeder-affixed twisted pair line 97 has two twisted pair lines, and signals of two lines exist in the feeder-affixed twisted pair line 97. The code conversion circuit 92 has a function of converting the signals of two lines to signals of one line so that the signals of two lines can be transmitted through the optical fiber 99 when an optical transmission is outputted, and a function of converting the optical signals of one line thus received to signals of two lines so that the signals can be transmitted on a twisted pair line.
The peak hold circuit 93 has a function of detecting the presence or absence of an optical signal on the basis of the electrical signal which is converted from the optical signal by the optical receiver 95, and a function of controlling the bias circuit 91 on the basis of the detection result. The bias circuit 91 has a function of applying a bias voltage to each twisted pair line 912a and 912b of the feeder-affixed twisted pair line 97 connected to the electric connector 98, and it is controlled on the basis of the output of the peak hold circuit 93. Specifically, when it receives an optical signal, it applies a bias voltage to the twisted pair line 912a and 912b, and when it receives no optical signal, it stops the voltage application, whereby a terminal device can detect insertion/removal of a feeder-affixed twisted pair line 912a and 912b or insertion/removal of an optical fiber 99a and 99b to initialize the IEEE1394 serial bus.
Further, a communication system based on optical or electrical waves by using space as a medium may be utilized from the viewpoint that rewiring due to movement of terminal devices or arrangement of twisted pair lines (cables) in a wiring process spoils the beauty of the appearance. The radio transmission system based on optical technique is called as xe2x80x9coptical spatial transmission systemxe2x80x9d, and it is described in xe2x80x9cFUNDAMENTALS OF OPTOELECTRONICSxe2x80x9d p. 26 issued by Keigaku Publication Co., Ltd., for example.
FIG. 12 is a block diagram showing an optical spatial transmission device disclosed in Japanese Laid-open Patent Application No. Hei-7-183849. The construction and operation of the optical spatial transmission device will be briefly described with reference to FIG. 12.
In the optical spatial transmission device of FIG. 12, a transmitter 101 includes an encode circuit 102 for converting an input information signal to a base band code, a driver circuit 103 for driving a optical emission unit 104 on the basis of the base band code, and the optical emission unit 104 for converting an electrical signal from the driver circuit 103 to an optical signal and discharging the optical signal to space. A receiver 105 includes a optical reception unit 106 for receiving the optical signal from a spatial transmission path and converting the received optical signal to an electrical signal, a clock reproducing circuit 107 for reproducing a clock signal from the received optical signal, and a decode circuit 108 for reproducing a base band code from the reproduced clock signal and the electrical signal from the optical receiving unit 106, and outputting an information signal.
In order to solve the rewiring problem due to motion of terminal devices and the appearance-spoiling problem due to the arrangement of cables in the above-described prior art, it is considered that the optical spatial transmission system is applied to the optical transmission/reception portion of the optical transceiver of FIG. 11. In this case, when the optical communication path is intercepted in the neighborhood of the optical receiving unit and reflected optical is incident to the optical receiving unit, the optical spatial transmission device receives the reflection signal and thus cannot detect the interception of the communication path. Therefore, erroneous data are delivered to a terminal device, and thus the terminal device operates abnormally.
An object of the present invention is to provide a spatial transmission optical transceiver which can transmit/receive an optical signal through space serving as a communication medium between terminal devices in a network in which plural terminal devices are connected to one another through a data transmission line based on IEEE1394.
In order to attain the above object, a spatial transmission optical transceiver according to the present invention is characterized by detecting interception of a communication path and insertion/removal of a data transmission line connected to a confronting optical transceiver for spatial transmission.
Particularly, even when the optical transceiver for spatial transmission receives reflected optical due to interception of a communication path in the neighborhood of a optical transceiver, the spatial transmission optical transceiver of the present invention detects the interception of the communication path. Specifically, the spatial transmission optical transceiver according to the present invention includes optical signal detection means for detecting the presence or absence of an optical signal on a spatial transmission path, and reflection signal detecting means for detecting that a reception signal is a reflection signal on the basis of a transmitted/received signal.
Further, the spatial transmission optical transceiver according to the present invention is characterized by detecting the interception of the communication path or the insertion/removal of a signal line and notifying the detection result to a terminal device. Specifically, there is also provided with communication path interception/signal line insertion/removal notifying means for detecting the interception of the communication path and the insertion/removal of the data transmission line connected to the confronting spatial transmission optical transceiver are detected, and notifying the detection result to the terminal device.
According to the present invention, the insertion/removal of the data transmission line connected to the confronting spatial transmission optical transceiver and the interception of the communication path can be detected on the basis of the presence or absence of the optical signal. Further, the interception of the communication path can be detected by detecting the reflection signal due to the interception of the communication path in the neighbor of the spatial transmission optical transceiver. When there is no reception signal, it is judged that the data transmission line is removed or the communication path is intercepted, and this fact is notified to the terminal device. Further, even when the reflection optical of the transmission optical signal is incident to the optical transceiver due to the interception of the communication path in the neighborhood of the optical transceiver, the received optical signal is detected to be a reflection signal to thereby detect the interception of the communication path, and this fact is notified to the terminal device, whereby the terminal device can detect the insertion/removal of the data transmission line and the interception of the communication path, and thus a reset signal serving as a sign to initialize the network.